The present invention relates to wireless communication systems in general, and more particularly to methods and apparatus for implementing a distributed antenna system in an in-building cellular telephone system.
In-building cellular networks often require the use of multiple base transmission stations (BTS) located much closer together than outdoor BTSs. These in-building BTSs may employ a distributed antenna system where all segments radiate RF energy in order to provide coverage to mobile stations (MS). Such a prior art BTS arrangement is shown with respect to FIG. 1 which shows a BTS 10 having a distributed antenna 12 that is comprised of multiple radiant segments 14, 16, 18, and 20. Segments 14-20 typically transmit with equal power to an MS 22. Unfortunately, such an arrangement is inefficient as radiant segments 14, 16, and 20 that are farther from MS 22 radiate with equal power as segment 18 which is closest to MS 22.
BTS 10 is also prone to interference with and from other BTSs operating on the same frequency and at sufficient power that MSs receive more than one co-channel signal at the same time, thus limiting frequency reuse and network capacity. One way of overcoming this interference is by reducing the power transmitted by the BTSs. Unfortunately, reducing the transmission power also reduces the signal strength received by the MSs being served.
The present invention seeks to provide improved methods and apparatus for implementing a distributed antenna system in an in-building cellular telephone system in a manner that overcomes disadvantages of the prior art. The present invention discloses localizing RF power between an MS and the antenna segment to which it is closest, thereby improving network capacity by reducing interference between BTSs.
There is thus provided in accordance with a preferred embodiment of the present invention a distributed antenna system for use in an in-building cellular telephone network, the system including a base transmission station (BTS), and a distributed antenna for conveying transmissions to and from the BTS, the distributed antenna including a plurality of serially-interconnected radiant segments, and at least one delay element intermediate two of the plurality of radiant segments, where the delay element is operative to introduce a delay in a transmission between the BTS and a mobile station (MS), where the BTS is operative to discern the delay in the transmission and thereby determine which of the plurality of radiant segments is closest to the MS and selectively radiate RF energy via the closest segment and prevent the radiation of RF energy via any other of the plurality of radiant segments.
Further in accordance with a preferred embodiment of the present invention at least one delay element includes a plurality of delay elements and at least one of the plurality of delay elements is intermediate every two of the plurality of radiant segments.
Still further in accordance with a preferred embodiment of the present invention the BTS is additionally operative to instruct the MS to transmit in accordance with a timing advance in proportion to the delay.
Additionally in accordance with a preferred embodiment of the present invention the delay is sufficient to require the timing advance.
Moreover in accordance with a preferred embodiment of the present invention the delay is sufficient to cause a round trip delay that is greater than or equal to at least one step of the BTS equalizer timing resolution.
Further in accordance with a preferred embodiment of the present invention the delay element includes a transmission channel including at least one first delay component for receiving a transmission signal from a BTS, a first amplifier for receiving the transmission signal from the delay component, a first antenna for receiving the transmission signal from the first amplifier, and a switch for selectably controlling the receipt of the transmission signal at the antenna, a reception channel including a second antenna for receiving a reception signal, a power combiner for combining the reception signal and at least one other reception signal received via an third antenna, a second amplifier for receiving the reception signal from the power combiner, and at least one second delay component for receiving the reception signal from the second amplifier, and an antenna selector for selectably controlling the switch.
There is also provided in accordance with a preferred embodiment of the present invention a method for implementing a distributed antenna system in an in-building cellular telephone system having a base transmission station (BTS) and a distributed antenna including a plurality of serially-interconnected radiant segments for conveying transmissions to and from the BTS, the method including the steps of introducing a delay in a transmission between the BTS and a mobile station (MS) for each traversal of the transmission via any of the plurality of serially-interconnected radiant segments, discerning the delay in the transmission, thereby determining which of the plurality of radiant segments is closest to the MS, and selectively radiating RF energy via the closest segment and preventing the radiation of RF energy via any other of the plurality of radiant segments.
There is additionally provided in accordance with a preferred embodiment of the present invention a distributed antenna system for use in an in-building cellular telephone network, the system including a first and a second base transmission station (BTS), and a distributed antenna for conveying transmissions to and from either of the BTSs, the distributed antenna including a plurality of serially-interconnected radiant segments, at least one delay element intermediate two of the plurality of radiant segments, the delay element operative to introduce a delay in a transmission between the BTS and a mobile station (MS), and at least one switch intermediate two of the plurality of radiant segments, the delay element operative to actuate the switch, thereby disconnecting at least one of the plurality of radiant segments from either one of the BTSs where the either of the BTSs are operative to discern the delay in the transmission and thereby determine which of the plurality of radiant segments is closest to the MS, determine which of the BTSs lacks the capacity to accommodate the MS, and cause the delay element to actuate the switch thereby disconnecting the closest segment from the BTS lacking capacity.
Further in accordance with a preferred embodiment of the present invention either of the BTSs are operative to, if the BTS has capacity, selectively radiate RF energy via the closest segment and prevent the radiation of RF energy via any other of the plurality of radiant segments.
Still further in accordance with a preferred embodiment of the present invention at least one delay element includes a plurality of delay elements and at least one of the plurality of delay elements is intermediate every two of the plurality of radiant segments.
Additionally in accordance with a preferred embodiment of the present invention either of the BTSs is additionally operative to instruct the MS to transmit in accordance with a timing advance in proportion to the delay.
Moreover in accordance with a preferred embodiment of the present invention the delay is sufficient to require the timing advance.
Further in accordance with a preferred embodiment of the present invention the delay is sufficient to cause a round trip delay that is greater than or equal to at least one step of the BTS equalizer timing resolution.
Still further in accordance with a preferred embodiment of the present invention the delay element includes a transmission channel including at least one first delay component for receiving a transmission signal from a BTS, a first amplifier for receiving the transmission signal from the delay component, a first antenna for receiving the transmission signal from the first amplifier, and a switch for selectably controlling the receipt of the transmission signal at the antenna, a reception channel including a second antenna for receiving a reception signal, a power combiner for combining the reception signal and at least one other reception signal received via an third antenna, a second amplifier for receiving the reception signal from the power combiner, and at least one second delay component for receiving the reception signal from the second amplifier, and an antenna selector for selectably controlling the switch.
There is also provided in accordance with a preferred embodiment of the present invention a method for implementing a distributed antenna system in an in-building cellular telephone system having at least two base transmission stations (BTS) sharing an intermediate distributed antenna including a plurality of serially-interconnected radiant segments for conveying transmission to and from the BTSs, the method including the steps of introducing a delay in a transmission between either of the BTSs and a mobile station (MS) for each traversal of the transmission via any of the plurality of serially-interconnected radiant segments, discerning the delay in the transmission, thereby determining which of the plurality of radiant segments is closest to the MS, determining which of the BTSs lacks the capacity to accommodate the MS, and disconnecting the closest segment from the BTS lacking capacity.
It is noted throughout the specification and claims that the term xe2x80x9cclosest toxe2x80x9d as regards the relationship between an MS and a radiant antenna segment as described hereinbelow refers the segment which receives the strongest signal from the MS and which may or may not be physically closest to the MS than other segments.